The effect of sulfur on deactivation of palladium catalysts for methane oxidation has been investigated in this research. A PdO deactivation mechanism due to sulfur is proposed over the 100-400 degrees C range. H2S induced catalyst poisoning of PdO/gamma Al2O3 is attributed to the formation of aluminum sulfate. Catalyst activity decreases with increasing H2S deposition and increasing temperature from 100 to 400 degrees C. TGA results show that PdO promotes the reaction of H2S with gamma-Al2O3. Surface sulfite and sulfate groups are observed by FT-IR on poisoned catalysts and are believed to be the cause of a 25% decrease in BET surface area. Activation energy for methane oxidation of H2S poisoned catalyst decreases due to the formation of Al-2(SO4)(3) which causes the reaction to change from surface reaction control to pore-diffusion control. H-2 treatment at 600 degrees C removes much of the sulfite and sulfate from the surface of poisoned catalysts and regenerates most of the fresh catalyst activity.